TCP_KEEP* constants are netbsd specific

they doesn't exists on OpenBSD. put them under NetBSD specific tree.

Author: semarie

src/unix/bsd/netbsdlike/mod.rs

@@ -430,10 +430,6 @@ pub const IPV6_RECVPKTINFO: ::c_int = 36;
 pub const IPV6_PKTINFO: ::c_int = 46;
 
 pub const TCP_NODELAY:    ::c_int = 0x01;
-pub const TCP_KEEPIDLE:   ::c_int = 3;
-pub const TCP_KEEPINTVL:  ::c_int = 5;
-pub const TCP_KEEPCNT:    ::c_int = 6;
-pub const TCP_KEEPINIT:   ::c_int = 7;
 
 pub const SOL_SOCKET: ::c_int = 0xffff;
 pub const SO_DEBUG: ::c_int = 0x01;

src/unix/bsd/netbsdlike/netbsd/mod.rs

@@ -381,6 +381,11 @@ pub const IP_RECVPKTINFO: ::c_int = 26;
 pub const IPV6_JOIN_GROUP: ::c_int = 12;
 pub const IPV6_LEAVE_GROUP: ::c_int = 13;
 
+pub const TCP_KEEPIDLE:  ::c_int = 3;
+pub const TCP_KEEPINTVL: ::c_int = 5;
+pub const TCP_KEEPCNT:   ::c_int = 6;
+pub const TCP_KEEPINIT:  ::c_int = 7;
+
 pub const SOCK_CONN_DGRAM: ::c_int = 6;
 pub const SOCK_DCCP: ::c_int = SOCK_CONN_DGRAM;
 pub const SOCK_NOSIGPIPE: ::c_int = 0x40000000;